That’s the sort of place that geologists say might hold evidence of past life, which is high on the scientific agenda for the rover that’s due to be launched in 2020.

The hills in Mars’ Gusev Crater were named in honor of the space shuttle Columbia and its astronauts, all lost in a catastrophic breakup that occurred a year before Spirit’s landing in 2004. The twin Spirit and Opportunity rovers explored different parts of the Martian terrain for years. Spirit finally gave up the ghost in 2010, while Opportunity is still plugging along on the other side of the Red Planet.

The 2020 rover, which has yet to be given its official name, is being built on the basic design of the bigger and more capable Curiosity rover, which landed in a different crater in 2012. It’ll be outfitted with a new set of instruments optimized for assessing the site’s habitability, looking for signs of ancient Mars life, and potentially blazing a trail for human explorers.

One of its jobs will be to collect samples of rocks and soil and store them for their potential return to Earth during a follow-up mission. That adds to the importance of picking the right site.

Late last week, during a workshop in Monrovia, Calif., experts narrowed down the list of potential sites from eight to three. Here are the two alternatives to Columbia Hills in Gusev Crater:

Jezero Crater: Based on orbital imagery, scientists suspect that water filled up and drained away this crater on at least two occasions. More than 3.5 billion years ago, river channels spilled over the cratrer wall and created a lake. The wet conditions back then might have supported microbial life.

NE Syrtis Major: This layered terrain shows signs of being warmed by volcanic activity in ancient times. Underground heat sources might have given rise to hot springs and melting ice on the surface. If the conditions were right, microbes might have flourished in liquid water that came in contact with the region’s minerals.

The three finalist sites will undergo closer review in preparation for final site selection. Columbia Hills could be a controversial choice: Over the weekend, Nature reported that the idea of revisiting that site received a low rating from scientists at the workshop.

It’s likely to take more than a year for NASA to sort out which site is likely to offer the biggest potential scientific return, and place its bet for 2020. When the Curiosity mission went through its planning process, Gale Crater was unveiled as the landing site a year before launch.

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